1. Field of the Invention
The present invention relates to objective lens actuators and methods for producing the objective lens actuators, and more specifically to an objective lens actuator to actuate an objective lens for gathering light in a tracking direction and a focus direction relative to a disk-like recording medium such as a MD (mini disc), a CD (compact disc) and a DVD (digital versatile disc), and a method for producing the objective lens a actuator.
2. Description of the Background Art
It is known that an optical disk unit which records and/or reproduces information in/from a disk-like recording medium such as a MD, a CD and a DVD (hereinafter, referred to as an optical disk) is provided with an objective lens actuator for actuating an objective lens which gathers light emitted from a laser light source to apply the light to a recording surface of the optical disk. The objective lens actuator actuates the objective lens on two axes, which are a direction perpendicular to the recording surface of the optical disk (hereinafter, referred to as a focus direction) and a radial direction parallel with the recording surface (hereinafter, referred to as a tracking direction), in order to correct displacement of focus caused by up-and-down movements due to warpage of the optical disk and displacement of tracking caused by decentering and so forth.
FIG. 8 is a perspective view showing a structure of a conventional objective lens actuator disclosed in Japanese Patent Laying-Open No. 8-306059. In FIG. 8, the conventional objective lens actuator includes an objective lens 1, a lens holder 2, a focus coil 3, tracking coils 4a and 4b, wires 5a.about.5d, a stationary member 6, a magnet 7 and a yoke 8.
The lens holder 2 holding the objective lens 1 is movably supported by the stationary member 6 through the elastic metal wires 5a.about.5d. That is, the lens holder 2 can move on two axes, which are a focus direction F and a tracking direction T, by the wires 5a.about.5d which are placed in almost parallel with each other, one ends of which are installed to the lens holder 2 and the other ends of which are installed to the stationary member 6. The stationary member 6 is installed on the yoke 8. The magnet 7 secured on the yoke 8 forms a magnetic circuit cooperating with the yoke 8 to apply a magnetic field to the focus coil 3 and the tracking coils 4a and 4b. The focus coil 3 is fixed to the lens holder 2 and generates an actuation force to actuate the lens holder 2 in the focus direction F. The tracking coils 4a and 4b are fixed to the lens holder 2 and generate the actuation force to actuate the lens holder 2 in the tracking direction T.
Next, operation of the objective lens actuator composed as described in the above will be explained. The actuation force to the focus direction F is generated by a current being applied to the focus coil 3 which is placed within voids of the magnetic circuit formed by the magnet 7 and the yoke 8 and is fixed to the lens holder 2. By the generated actuation force to the focus direction F, the lens holder 2 slidably moves to the focus direction F through the four parallel wires 5a.about.5d. On the other hand, the actuation force to the tracking direction T is generated by a current being applied to the tracking coils 4a and 4b which are placed within voids of the magnetic circuit formed by the magnet 7 and the yoke 8 and are fixed to the lens holder 2. By the generated actuation force to the tracking direction T, the lens holder 2 moves to the tracking direction T parallel to itself through the four parallel wires 5a.about.5d.
In the objective lens actuator composed as described in the above, the lens holder 2, the stationary member 6 and the wires 5a.about.5d are integrally molded (for example, refer to the Japanese Patent Laying-Open No. 8-87766), which leads to such advantages that the objective lens actuator is easy to be assembled and a position of each component becomes more precise. However, the objective lens actuator has a problem that the wires 5a.about.5d are deformed by injection pressure of a material at a time of molding to degrade performance of the objective lens actuator.
The above-mentioned problem will be described below. FIG. 9.about.FIG. 11 are top plan views of main portions showing states of molding in a step-by-step manner. FIG. 9 shows the lens holder 2, the stationary member 6 and the wires 5a.about.5d which are integrally molded, gate positions of a mold to which an injection material is injected (illustrated by black points), directions of material flowing in the mold (illustrated by arrows) and a range of a main portion of the mold (illustrated by diagonally shaded areas). When the objective lens actuator is molded by the mold as shown in FIG. 9, there is a possibility that the wires (only the wires 5a and 5c are illustrated in FIG. 10) are deformed at the time of molding at connecting portions between the wires and the lens holder 2 and at connecting portions between the wires and the stationary member 6. In a case of such deformation, since the wires are not parallel with each other after the mold is removed as shown in FIG. 11, such problems occur as inclination of a motion axis of lens holder 2 during actuation and degradation of frequency response characteristic.